High intensity discharge (HID) and fluorescent lamps often undergo undesirable behavior patterns as they approach failure. Fluorescent lamps frequently flicker, swirl, and go off and on. High pressure sodium (HPS) lamps cycle off and on and arc within the lamp envelope. Some metal halide (MH) lamps explode and can generate a significant hazard. Most of this behavior is not only annoying to individuals working in the vicinity of such lamps but is also destructive to the ballast and other electrical components because the erratic behavior produces current and voltage surges and transients which accelerate failure of the dielectric components associated with the ballast, the electronic components, lead wires, sockets, lamp parts, etc. Also, as indicated above, the undesirable nature of this behavior goes beyond fixture reliability and life reduction especially in the case of the metal halide lamps which have been known to explode and drop hot lamp pieces which are capable of burning individuals and starting fires. Manufacturers of such lamps have therefore specified the use of glass doors in fixtures which employ MH lamps which increases the fixture cost and decreases the optical efficiency.
It is also possible for such lamp explosions to release the chemicals within the lamp, such as mercury, into the immediate environment, creating a possible toxicity problem.
At the very best, HPS lamps cycle on and off, creating an obnoxious lighting situation. When an HPS lamp is used for street lighting purposes, this cycling action makes visual direction of a failing HPS lamp a problem because when it is on it appears to be quite normal and a passing patrol car may not observe that cycling activity. Thus, the lamp can go through a number of on-and-off states before it is finally observed in the off state. During this time, the ballast is still energized and consuming electrical energy while not illuminating properly. All of the above leads to dissatisfaction with lighting systems using such lamps and also to increased maintenance costs.